Dual fuel injection system

ABSTRACT

A method of controlling fuel injection in a dual fuel engine system includes determining, with a first controller, a diesel injection pulse indicative of a first amount of diesel fuel to be injected into a combustion chamber of the engine and a first timing at which the first amount of diesel fuel is to be injected. The method also includes determining, with a second controller, a combined injection pulse based on the diesel injection pulse. The method further includes injecting the second amount of diesel fuel and the third amount of natural gas into the combustion chamber in accordance with the combined injection pulse. In such a method, injection in accordance with the combined injection pulse results in a combustion event characterized by a second combustion characteristic substantially equal to a first combustion characteristic associated with the diesel injection pulse.

TECHNICAL FIELD

The present disclosure relates generally to a fuel system and, moreparticularly, to a dual fuel system for use with an internal combustionengine.

BACKGROUND

Many different systems exist for delivering fuel into an engine'scombustion chambers. For example, liquid and/or gaseous fuel can bedirectly injected into the combustion chamber, or indirectly injectedinto an upstream air passage and allowed to mix with air as the airenters the combustion chamber. In either situation, it can be achallenge to maximize combustion and/or fuel efficiency across allengine operating conditions while, at the same time, meeting emissionsrequirements associated with combustion exhaust. These challenges areamplified for applications in which more than one fuel is beingcombusted. For example, in such dual fuel applications, it can bedifficult to optimize the amount of each fuel injected, as well as thetiming of such injections, such that fuel efficiency is maximized.Additionally, dual fuel injection strategies directed toward maximizingfuel efficiency may not necessarily minimize levels of harmfulpollutants present in engine exhaust.

The disclosed system is directed to overcoming one or more of theproblems set forth above and/or other problems of the prior art.

SUMMARY

In an exemplary embodiment of the present disclosure, a method ofcontrolling fuel injection in a dual fuel engine system includesdetermining, with a first controller, a diesel injection pulseindicative of a first amount of diesel fuel to be injected into acombustion chamber of the engine and a first timing at which the firstamount of diesel fuel is to be injected. The diesel injection pulse isbased on a set of operating parameters associated with the engine, andfuel injection in accordance with the diesel injection pulse wouldresult in a first combustion characteristic within the combustionchamber sufficient to satisfy an output demanded of the engine usingsolely diesel fuel. The method also includes determining, with a secondcontroller, a combined injection pulse based on the diesel injectionpulse. The combined injection pulse is indicative of a second amount ofdiesel fuel to be injected different than the first amount, a secondtiming at which the second amount of diesel fuel is to be injecteddifferent than the first timing, a third amount of natural gas to beinjected, and a third timing at which the third amount of natural gas isto be injected. The method further includes injecting the second amountof diesel fuel and the third amount of natural gas into the combustionchamber in accordance with the combined injection pulse. The injectionin accordance with the combined injection pulse results in a combustionevent characterized by a second combustion characteristic substantiallyequal to the first combustion characteristic.

In another exemplary embodiment of the present disclosure, a method ofcontrolling fuel injection in a dual fuel engine system includesreceiving, from a sensor, a first signal indicative of at least oneoperating parameter associated with a dual fuel engine of the system,and determining, with a control system, a diesel injection pulseindicative of a first amount of diesel fuel to be injected into acombustion chamber of the engine and a first timing at which the firstamount of diesel fuel is to be injected. The diesel injection pulse isdetermined based on the at least one operating parameter, and fuelinjection in accordance with the diesel injection pulse would result ina first combustion characteristic within the combustion chambersufficient to satisfy an output demanded of the engine using solelydiesel fuel. The method also includes generating, with the controlsystem, a second signal indicative of the diesel injection pulse, anddetermining, with the control system, a combined injection pulse basedon the second signal. The combined injection pulse is indicative of asecond amount of diesel fuel to be injected different than the firstamount, a second timing at which the second amount of diesel fuel is tobe injected different than the first timing, a third amount of naturalgas to be injected, and a third timing at which the third amount ofnatural gas is to be injected. The method further includes directing athird signal indicative of the combined injection pulse to an injectionsystem associated with the engine, and injecting, with the injectionsystem, the second amount of diesel fuel and the third amount of naturalgas into the combustion chamber in accordance with the combinedinjection pulse. The injection in accordance with the combined injectionpulse results in a combustion event characterized by a second combustioncharacteristic substantially equal to the first combustioncharacteristic. Additionally, the diesel injection pulse determined bythe control system is unaffected by the second amount, the secondtiming, the third amount, and the third timing.

In a further exemplary embodiment of the present disclosure, a dual fuelengine system includes a sensor configured to determine at least oneoperating parameter associated with a dual fuel engine of the system,and a first controller in communication with the sensor, the firstcontroller configured to determine a diesel injection pulse indicativeof a first amount of diesel fuel to be injected into a combustionchamber of the engine and a first timing at which the first amount ofdiesel fuel is to be injected. The diesel injection pulse is determinedbased on the at least one operating parameter, and fuel injection inaccordance with the diesel injection pulse would result in a firstcombustion characteristic within the combustion chamber sufficient tosatisfy an output demanded of the engine using solely diesel fuel. Thesystem also includes a second controller in communication with the firstcontroller, the second controller configured to determine a combinedinjection pulse based on the diesel injection pulse. The combinedinjection pulse is indicative of a second amount of diesel fuel to beinjected different than the first amount, a second timing at which thesecond amount of diesel fuel is to be injected different than the firsttiming, a third amount of natural gas to be injected, and a third timingat which the third amount of natural gas is to be injected. The systemfurther includes an injection system in communication with the secondcontroller and fluidly connected to the combustion chamber. Theinjection system is configured to inject the second amount of dieselfuel and the third amount of natural gas into the combustion chamber inaccordance with the combined injection pulse. The injection inaccordance with the combined injection pulse results in a combustionevent characterized by a second combustion characteristic substantiallyequal to the first combustion characteristic, and the diesel injectionpulse determined by the first controller is unaffected by the secondamount, the second timing, the third amount, and the third timing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an illustration of an exemplary dual fuel engine system.

FIG. 2 is an illustration of a dual fuel engine associated with thesystem shown in FIG. 1.

FIG. 3 is a flowchart illustrating an exemplary method of the presentdisclosure.

FIG. 4 is an exemplary pressure pulse diagram associated with the systemof FIG. 1.

FIG. 5 illustrates exemplary lookup tables associated with the system ofFIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary dual fuel engine system 100 of thepresent disclosure, including an exemplary engine 10. For the purposesof this disclosure, engine 10 is depicted and described as a dual fuelinternal combustion engine, such as an internal combustion engineconfigured to combust diesel and natural gas, or a mixture thereof.However, it is contemplated that engine 10 may embody any other type ofcombustion engine such as, for example, a diesel engine, a gasolineengine, or a gaseous fuel-powered engine burning compressed or liquefiednatural gas, propane, or methane. Engine 10 may include an engine block12 at least partially defining a plurality of cylinders 14. As will bedescribed with respect to FIG. 2, engine 10 may also include a pluralityof piston assemblies disposed within respective cylinders 14 to form aplurality of combustion chambers. It is contemplated that engine 10 mayinclude any number of combustion chambers and that the combustionchambers may be disposed in an in-line configuration, in a “V”configuration, in an opposing-piston configuration, or in any otherconventional configuration.

Multiple separate sub-systems may be associated within engine 10 andsuch sub-systems may cooperate to facilitate the production of power.For example, system 100 may include an air induction system 16, anexhaust system 18, an aftertreatment system 20, a fuel system 36, and acontrol system 50. Air induction system 16 may be configured to directair or an air and fuel mixture into engine 10 for subsequent combustion.Fuel system 36 may be configured to direct one or more fuels, or amixture of fuels, to either the air induction system 16 or directly tothe combustion chambers. Exhaust system 18 may exhaust byproducts ofcombustion to the atmosphere. Aftertreatment system 20 may function toreduce the discharge of regulated constituents by engine 10 to theatmosphere. Control system 50 may be in communication with engine 10 andwith components of each of the air induction system 16, exhaust system18, aftertreatment system 20, and fuel system 36, and may be configuredto control operation of such components.

Air induction system 16 may include multiple components configured tocondition and introduce compressed air into cylinders 14. For example,air induction system 16 may include an air cooler 22 located downstreamof one or more compressors 24. Compressors 24 may be connected topressurize inlet air directed through cooler 22. It is contemplated thatair induction system 16 may include different or additional componentsthan described above such as, for example, a throttle valve, variablevalve actuators associated with each cylinder 14, filtering components,compressor bypass components, exhaust gas recirculation components,and/or other known components that may be selectively controlled toaffect an air-to-fuel ratio of engine 10, if desired. It is furthercontemplated that compressor 24 and/or cooler 22 may be omitted, if anaturally aspirated engine is desired.

Exhaust system 18 may include multiple components that condition anddirect exhaust from cylinders 14 to the atmosphere. For example, exhaustsystem 18 may include an exhaust passage 26 and one or more turbines 28driven by exhaust flowing through passage 26. It is contemplated thatexhaust system 18 may include different or additional components thandescribed above such as, for example, bypass components, an exhaustcompression or restriction brake, an attenuation device, and other knowncomponents, if desired.

Turbine 28 may be located to receive exhaust leaving engine 10, and maybe connected to one or more compressors 24 of air induction system 16 byway of a common shaft to form a turbocharger. As the hot exhaust gasesexiting engine 10 move through turbine 28 and expand against vanes (notshown) thereof, turbine 28 may rotate and drive the connected compressor24 to pressurize inlet air.

Aftertreatment system 20 may include components configured to trap,catalyze, reduce, or otherwise remove regulated constituents from theexhaust flow of engine 10 prior to discharge to the atmosphere. Forexample, aftertreatment system 20 may include a reduction device 30fluidly connected downstream of turbine 28.

Reduction device 30 may receive exhaust from turbine 28 and reduceparticular constituents of the exhaust. In one example, reduction device30 is a Selective Catalytic Reduction (SCR) device having one or moreserially-arranged catalyst substrates 32 located downstream from areductant injector (not shown). A gaseous or liquid reductant, mostcommonly urea ((NH₂)₂CO), a water/urea mixture, a hydrocarbon such asdiesel fuel, or ammonia gas (NH₃), may be sprayed or otherwise advancedinto the exhaust within passage 26 at a location upstream of catalystsubstrate(s) 32 by the reductant injector. This process of injectingreductant upstream of catalyst substrate 32 may be known as “dosing”catalyst substrate(s) 32. To facilitate dosing of catalyst substrate(s)32 an onboard supply of reductant, a pressurizing device, and/or otherlike components (not shown) may be associated with the reductantinjector and/or the substrate 32. The reductant sprayed into passage 26may flow downstream with the exhaust from engine 10 and be adsorbed ontothe surface of catalyst substrate(s) 32, where the reductant may reactwith NO_(X) (NO and NO₂) in the exhaust gas to form water (H₂O) andelemental nitrogen (N₂). This reduction process performed by reductiondevice 30 may be most effective when a concentration of NO to NO₂supplied to reduction device 30 is about 1:1.

To help provide the correct concentration of NO to NO₂, an oxidationcatalyst 34 may be located upstream of reduction device 30, in someembodiments. Oxidation catalyst 34 may be, for example, a dieseloxidation catalyst (DOC). As a DOC, oxidation catalyst 34 may include aporous ceramic honeycomb structure or a metal mesh substrate (not shown)coated with a material, for example a precious metal, which catalyzes achemical reaction to alter the composition of the exhaust. For instance,oxidation catalyst 34 may include a washcoat of palladium, platinum,vanadium, or a mixture thereof that facilitates the conversion of NO toNO₂.

In one embodiment, oxidation catalyst 34 may also perform particulatetrapping functions. That is, oxidation catalyst 34 may be a catalyzedparticulate trap such as a continuously regeneration particulate trap ora catalyzed continuously regenerating particulate trap. A particulatetrap is a filter designed to trap or collect particulate matter. Infurther exemplary embodiments, the oxidation catalyst 34 may be aseparate component disposed upstream or downstream of a particulate trapin the exhaust system 18.

Fuel system 36 includes first and second fuel sources 38, 40, respectivefuel lines 42, 44, fluidly connecting fuel sources 38, 40 to cylinders14, and one or more respective fuel pumps, valves, restrictors, mixers,accumulators, filters, and/or other known fuel delivery components 46,48 configured to pressurize, regulate, clean, and/or controllably directfuel from the first and second fuel sources 38, 40 to the respectivecylinders 14. Such components 46, 48 may be configured for use with anyof the liquid and/or gaseous fuels described herein.

First and second fuel sources 38, 40 may comprise fuel tanks or othercontainers (e.g., pressurized cylinders) suitable to serve as areservoir for fuel. The fuel may be held within first and second fuelsources 38, 40 in gaseous or liquid form, as desired. In one example, ifheld as a liquid, fuel within first fuel source 38 may first begassified before being directed into fuel line 42. Gassification mayoccur through a change in pressure and/or application of heat to thefuel, and one or more components 46 fluidly connected to fuel line 42may assist with such gassification. In another example, if held as agas, fuel within second fuel source 40 may be maintained at an elevatedpressure, and may be controllably released using one or more controlvalves, or other like components 48 fluidly connected to fuel line 44.Additionally, in such embodiments, first and second fuel sources 38, 40may comprise one or more metals, alloys, composites, or other likematerials to assist in reinforcing one or more walls thereof in order tofacilitate safe storage, transportation, and release of pressurizedfuels.

Control system 50 may include one or more controllers in communicationwith engine 10 and/or components of the subsystems 16, 18, 20, 36described herein. In an exemplary embodiment, control system 50 mayinclude a first controller 52, and a second controller 54 incommunication with the first controller 52. One of the first and secondcontrollers 52, 54 may comprise an electronic control unit (ECU) of themachine to which engine 10 is connected. In such an embodiment, secondcontroller 54 may be added and/or otherwise connected to the machine andconfigured to communicate with an existing first controller 52, so as toreceive information from the first controller 52 but not inhibit thenormal function of the first controller 52. In such embodiments, secondcontroller 54 may be configured to receive one or more signalsoriginating from first controller 52, and to condition and/or otherwisemodify such signals. Alternatively, second controller 54 may utilizesuch signals as inputs into one or more control algorithms and/orprotocols, and may generate additional signals based on the signalsreceived from first controller 52. Additionally, first and secondcontrollers 52, 54 may be in communication with one or more sensors 56a, 56 b, 56 c, 56 d (collectively referred to as “sensors 56”). In suchembodiments, sensors 56 may generate signals indicative of one or moreoperating parameters of engine 10 and/or components of the subsystems16, 18, 20, 36. Sensors 56 may direct such signals to at least one offirst and second controllers 52, 54 for use as inputs into the one ormore control algorithms and/or protocols described herein. Theinteraction of, for example, sensors 56, control system 50, and fuelsystem 36 will be described in greater detail below.

FIG. 2 illustrates exemplary components of engine 10 in further detail.As shown in FIG. 2, a piston 58 may be slidably disposed within eachcylinder 14 to reciprocate between a top-dead-center (TDC) position anda bottom-dead-center (BDC) position, and a cylinder head 60 may beassociated with each cylinder 14. Cylinder 14, piston 58, and cylinderhead 60 may together define a combustion chamber 62 of engine 10. It iscontemplated that engine 10 may include any number of combustionchambers 62 and, as noted above, such combustion chambers 62 may bedisposed in an “in-line” configuration, in a “V” configuration, in anopposing-piston configuration, or in any other suitable configuration.

Engine 10 may also include a crankshaft 64 that is rotatably disposedwithin engine block 12. A connecting rod 66 may connect each piston 58to crankshaft 64 so that a sliding motion of piston 58 between the TDCand BDC positions within each respective cylinder 14 results in arotation of crankshaft 64. Similarly, a rotation of crankshaft 64 mayresult in a sliding motion of pistons 58 between the TDC and BDCpositions. As crankshaft 64 rotates through about 180 degrees (i.e., ascrankshaft 64 moves through one-half of its rotation), each piston 58may move through one full stroke between BDC and TDC. In embodiments inwhich engine 10 comprises a four-stroke engine, piston 58 mayreciprocate between the TDC and BDC positions during each of an intakestroke, a compression stroke, a combustion or power stroke, and anexhaust stroke (also known as a “piston cycle”) for every completeengine cycle or two full rotations of crankshaft 64. Thus, in exemplaryembodiments, each piston cycle of a four-stroke engine may include two360° rotations of crankshaft 64. In an alternative embodiment, engine 10may be a two-stroke engine, and may have a complete cycle that includesa power/exhaust/intake stroke (TDC to BDC) and an intake/compressionstroke (BDC to TDC). In such embodiments, a piston cycle of a two-strokeengine may include a single 360° rotation of crankshaft 64.

During a phase of the power/exhaust/intake stroke described, air may bedrawn into combustion chamber 62 via one or more air intake ports 68located within a sidewall of each cylinder 14 (e.g., within a liner ofeach cylinder 14). In particular, as piston 58 moves downward withincylinder 14, a position will eventually be reached at which air intakeports 68 are no longer blocked by piston 58 and instead are fluidlycommunicated with combustion chamber 62. When air intake ports 68 are influid communication with combustion chamber 62 and a pressure of air atair intake ports 68 is greater than a pressure within combustion chamber62, air will pass through air intake ports 68 into combustion chamber62.

Eventually, piston 58 will start an upward movement that blocks airintake ports 68 and compresses the air/fuel mixture. It is understoodthat the air/fuel mixture may comprise a mixture of air, liquid fuel,and gaseous fuel. As the air/fuel mixture within combustion chamber 62is compressed, a temperature and pressure of the mixture may increaseand, at a point when piston 58 is near TDC, the air/fuel mixture mayignite. This ignition may result in a release of chemical energy in theform of temperature and pressure spikes (also known as “pressurepulses”) within combustion chamber 62.

During a phase of the power/exhaust/intake stroke, the pressure pulsewithin combustion chamber 62 may force piston 58 downward, therebyimparting mechanical power to crankshaft 64. At a particular pointduring this downward travel, one or more exhaust ports (not shown)located within cylinder head 60 (or elsewhere) may open to allowpressurized exhaust within combustion chamber 22 to exit and the cyclewill restart.

Gaseous fuel (e.g., methane or natural gas), may be introduced intocombustion chamber 62 (e.g., radially injected) through at least one ofair intake ports 68. The gaseous fuel may mix with the air to form afuel/air mixture within combustion chamber 62. Alternatively, gaseousfuel may be injected into intake passage 25 of air induction system 16.For example, gaseous fuel may be injected into intake passage 25 betweencompressor 24 and air cooler 22, or downstream of air cooler 22, such asin an intake manifold of engine 10. In such embodiments at least onemixer (not shown) may be utilized to facilitate substantiallyhomogeneous mixing of the injected gaseous fuel with the intake air. Instill further embodiments, such as in a shared port intake system,gaseous fuel may be provided to multiple ports 68, substantiallysimultaneously, from a single source. In any of the embodimentsdescribed herein, one or more injectors 70 may be fluidly connected toeach cylinder 14, such as via one of more ports 68, to inject gaseousfuel into combustion chamber 62. Additionally, injectors 70 may befluidly connected to second fuel source 40 and components 48 via fuelline 44. In exemplary embodiments, injectors 70 may be fluidly connectedto second fuel source 40 and components 48 via a common fuel rail, orother like fuel manifold fluidly connected to fuel line 44.

In a similar way, liquid fuel (e.g., diesel or gasoline) may also beintroduced into combustion chamber 62 via a respective injector 72fluidly connected to each cylinder 14. For example, injectors 72 mayinject pressurized liquid fuel, at any desirable location withincombustion chamber 62, to facilitate substantially homogenous mixingwith gaseous fuel injected into combustion chamber 62 and/or thefuel/air mixture formed by the mixture of gaseous fuel and intake air.Additionally, injectors 72 may be fluidly connected to first fuel source38 and components 46 via fuel line 42. In exemplary embodiments,injectors 72 may be fluidly connected to first fuel source 38 andcomponents 46 via a common fuel rail, or other like fuel manifoldfluidly connected to fuel line 42. The respective timing and volume ofboth liquid and gaseous fuel injected into combustion chamber 62 may becontrolled by control system 50 and/or fuel system 36 to produce acombustion event within each combustion chamber 62 having desiredcharacteristics. Such control will be described in further detail below.

In one embodiment, each gaseous fuel injector 70 may be positionedadjacent the liner of a corresponding cylinder 14 at a particular airintake port 68, such that a nozzle of fuel injector 70 is in directcommunication with combustion chamber 62 via the air intake port 68. Inanother embodiment, one or more fuel injectors 70 may indirectlycommunicate with combustion chamber 62, for example, via a recess orcavity that functions as a distribution and/or mixing manifold at airintake ports 68. Likewise, each liquid fuel injector 72 may bepositioned adjacent the liner of a corresponding cylinder 14, and anozzle of each fuel injector 72 may be spaced from respective intakeports 68. Each respective nozzle of fuel injectors 72 may be in directfluid communication with combustion chamber 62, as desired, to affectproper injection and/or mixing of liquid fuel with gaseous fuel and/orair within the combustion chamber 62. Alternatively, one or more fuelinjectors 72 may indirectly communicate with combustion chamber 62, forexample, via the recess or cavity described above, that functions as adistribution and/or mixing manifold proximate air intake ports 68. Inexemplary embodiments, at least one of fuel injectors 70, 72 maycomprise a solenoid-actuated injector, and in further embodiments, atleast one of fuel injectors 70, 72 may employ one or more solenoids tocontrol the injection of fuel.

As shown in FIGS. 1 and 2, components 46, 48, sensors 56, and/or othercomponents of the system 100 may be controllably connected to one orboth of first and second controllers 52, 54 of control system 50.Controllers 52, 54 may embody a single or multiple microprocessors,field programmable gate arrays (FPGAs), digital signal processors(DSPs), etc., that include a means for controlling an operation of fuelsystem 36 in response to signals received from one or more sensors 50.Numerous commercially available microprocessors can be configured toperform the functions of controller 40. It should be appreciated thatcontrollers 52, 54 could readily embody a general engine microprocessorcapable of controlling numerous system functions and modes of operation.Various other known circuits may be associated with controllers 52, 54,including power supply circuitry, signal-conditioning circuitry,actuator driver circuitry (i.e., circuitry powering solenoids, motors,or piezo actuators), communication circuitry, and other appropriatecircuitry.

Sensors 50 may be configured to generate a signal indicative of anengine operating parameter and/or a set of operating parameters. In oneexample, the set of operating parameters may be associated with and/ormay otherwise include a speed of engine 10, a speed of a vehicle towhich engine 10 is connected, a load of engine 10, a temperature ofintake air directed to engine 10 via intake passage 25, a temperature ofambient air, a temperature of exhaust emitted by engine 10, and/or otherlike operating parameters. For example, sensor 56 a may be configured tomeasure, sense, and/or otherwise determine a temperature of ambient airor intake air. Sensor 56 b may be configured to measure, sense, and/orotherwise determine at least one of an exhaust temperature and anexhaust pressure. Sensor 56 c may be disposed proximate crankshaft 64,and configured to measure and generate a signal indicative of aninstantaneous angular position of crankshaft 64. Based on a change inthis position relative to time, a speed of engine 10 may be derived. Theposition information may also or alternatively be used to determine thepositions of pistons 58. Sensor 56 d may comprise one or more additionalsensors configured to determine, for example, accelerator pedalposition, brake pedal position, transmission gear selection, and/orother like operating parameters. Based on signals generated by sensor 56d, an output demanded of engine 10, such as a speed of engine 10, atorque generated by engine 10, an acceleration required of engine 10, adeceleration required of engine 10 and/or other like outputs may bedetermined by controllers 52, 54. Additionally, based on the enginespeed, piston positions, engine load, intake temperature, and/or otheroperating parameters described herein, as well as the one or moreoutputs demanded of engine 10, controllers 52, 54 may be configured todetermine a timing at which fuel should be injected into combustionchamber 62 and/or a quantity of fuel that should be injected.Controllers 52, 54 may selectively activate components 46, 48 to affectinjection of desired respective quantities of a first fuel and a secondfuel at desired respective timings in a piston cycle of the combustionchambers 62.

The disclosed embodiments may be applicable to any combustion enginewhere active and individualized control over separate fuel injectionevents is desired. For example, the disclosed dual fuel engine system100 may be used in association with a machine such as an over-the-roadvehicle, an off-road vehicle, and/or any other like machine used inconstruction, transportation, shipping, farming, mining, powergeneration, and/or other applications. Such machines may include, forexample, light-duty trucks/vehicles, heavy-duty trucks/vehicles, dozers,loaders, excavators, tractors, and the like.

In operation, engine 10 may combust a combination of fuels in order tosatisfy an output demanded of engine 10. System 100 may facilitateproviding engine 10 with corresponding amounts of a first fuel and asecond fuel, at specific respective timings during each piston cycle toaffect such an output. In exemplary embodiments, system 10 may be tunedand/or otherwise controlled such that a combustion characteristic (suchas a peak pressure within combustion chamber 10, a torque output of thecombustion chamber 10, a combustion of approximately 50 percent of thefuel within the combustion chamber 10 at a desired crank angle, and/or apeak combustion temperature within the combustion chamber 10) achievedby combusting the first and second fuels may be substantially equal to acorresponding combustion characteristic that would be achieved bycombustion of only the first fuel under like engine load/demandconditions. By injecting and combusting first and second fuels inaccordance with the strategies discussed herein, emission of particulatematter, and other harmful pollutants in the exhaust of engine 10 may bereduced without sacrificing engine performance. Indeed, due to the useof natural gas and other like “clean burning” fuels, in some situationsengine performance may be improved while emissions are reduced.Operation of system 100 will now be described in detail with respect toFIGS. 3-5.

As shown in the exemplary flowchart 200 illustrated in FIG. 3, at 202control system 50 and/or associated sensors 56 may determine one or moreoperating parameters associated with system 100. For example, sensors 56may measure, sense, calculate, and/or otherwise determine one or moreoperating parameters associated with engine 10, induction system 16,exhaust system 18, aftertreatment system 20, fuel system 36, and/orcomponents thereof. Each respective sensor 56 may direct one or morecorresponding signals indicative of such operating parameters to thecontrol system 50 for processing. For example, sensors 56 may determinea set of operating parameters including at least one of the travel speedof a vehicle to which engine 10 is connected, a load of engine 10, aspeed of engine 10, a temperature of intake air directed to engine 10 byinduction system 16, a temperature of exhaust emitted by engine 10, agear selection associated with a transmission connected to engine 10, aposition of an acceleration pedal and/or a brake pedal associated withengine 10, and/or other like parameters. It is understood that one ormore such operating parameters may be indicative of an output demandedof engine 10. For example, an operator of a vehicle to which engine 10is connected may demand a particular engine speed, engine torque, engineacceleration, engine deceleration, and/or other like engine outputs, andone or more of the operating parameters determined by sensors 56 may beindicative of such engine outputs. In particular, the position of theacceleration pedal and/or brake pedal associated with engine 10 may bean operating parameter that is indicative of engine speed, engineacceleration, or engine deceleration. At 202, sensors 56 may directsignals indicative of such operating parameters to one or both of firstand second controllers 52, 54. In an exemplary embodiment, such signalsmay initially be sent to first controller 52 for processing. In such anembodiment, first controller 52 may comprise an OEM ECU associated withengine 10. Since first and second controllers 52, 54 are communicativelyand/or operably connected, signals sent to first controller 52 may bepassed to or observed by second controller 54 in any known manner.

At 204, control system 50 may determine a diesel injection pulseindicative of a first amount of diesel fuel to be injected into one ormore combustion chambers 62 of engine 10, as well as a first timing atwhich the determined first amount of diesel fuel is to be injected. Forexample, first controller 52 may receive one or more of the signals fromsensors 56 described above and may, in response, determine the firstamount of diesel fuel and the first injection timing. As referred toherein, an “injection timing” may comprise a crank angle (i.e., arotational position and/or angle of crankshaft 64), a correspondingpiston location within cylinder 14 during a respective piston cycle, anelapsed time, with respect to TDC or BDC, associated with a respectivepiston cycle, and/or any other known timing indicators associated withmovement of crankshaft 64 or piston 58. Likewise, as referred to herein,an “amount” of fuel to be injected may comprise any volume of liquid orgaseous fuel. In exemplary embodiments, the diesel injection pulse maybe determined at 204 based on at least one of the operating parametersdescribed above. Additionally, it is understood that fuel injection inaccordance with the determined diesel injection pulse may result in afirst combustion characteristic within combustion chamber 62 sufficientto satisfy an output demanded of engine 10 using solely diesel fuel. Inparticular, the first diesel amount and first diesel timing associatedwith the diesel injection pulse may comprise the calculated (i.e.,demanded) fuel volume and injection timing required to meet the engineoutput requested by an operator using only diesel fuel. In embodimentsin which first controller 52 comprises an OEM ECU coupled to engine 10,the diesel injection pulse may comprise a standard single fuel outputsignal of the ECU without any modifications or adjustments made tooptimize dual fuel operation of engine 10.

As noted above, in exemplary embodiments a first combustioncharacteristic of the present disclosure may comprise a peak pressuregenerated within combustion chamber 62, a torque output from combustionchamber 62, and/or a particular crank angle at which a peak pressure ora desired torque output is generated within combustion chamber 62. Forexample, as illustrated in FIG. 4 engine 10 may be tuned such that, fora given engine speed, a pressure within cylinder 14 is maximized aspiston 58 is disposed proximate TDC. In particular, the exemplarypressure pulse plot 74 of FIG. 4 associated with operation of engine 10using only diesel fuel indicates that, for a given engine speed, apressure within cylinder 14 may be maximized at point A. Tuning engine10 such that approximately 50 percent of fuel within combustion chamber62 is combusted when piston 58 reaches the crank angle associated withpoint A may minimize the levels of harmful pollutants contained inengine exhaust. However, such engine tuning may not necessarily maximizethe fuel efficiency of engine 10 in all applications. It is understoodthat the crank angles at which maximum fuel efficiency and/or minimumemissions occurs may vary based on the size, type, and/or class ofengine, as well as the fuel or mixture of fuels being combusted. It isalso understood that that engine 10 may be tuned such that, for a givenengine speed, torque output of cylinder 14 is maximized as piston 58 isdisposed proximate TDC.

Natural gas, on the other hand, may combust at a different rate thandiesel fuel. For example, pressure pulse plot 76 associated withoperation of engine 10 using only natural gas indicates that, for givenengine speed, a pressure within cylinder 14 may be maximized at point B.It is understood that each of the crank angles described herein aremerely exemplary and/or approximate since, as noted above, the crankangles at which maximum fuel efficiency and/or minimum emissions occursmay vary based on the size, type, and/or class of engine, as well as thefuel or mixture of fuels being combusted. It is also understood thatthat engine 10 may be tuned such that, for a given engine speed, torqueoutput of cylinder 14 is maximized as piston 58 is disposed proximateTDC.

While engine 10 may be tuned to optimize fuel efficiency and/or tominimize emissions based on the combustion characteristics illustratedby respective pressure pulse plots 74, 76 when either diesel or naturalgas is used, combusting both diesel and natural gas efficiently duringthe same piston cycle requires separate control of the amount of dieselfuel injected into combustion chamber 62, the timing at which the dieselfuel is injected, the amount of natural gas injected into combustionchamber 62, and the timing at which the natural gas is injected. Inexemplary dual fuel embodiments, active control of the respective amountand timing of diesel and natural gas injection may enable system 100 tomatch the fuel efficiency, peak pressure, torque output, exhaustemissions characteristics, and/or other combustion characteristicsassociated with engine operation using solely diesel fuel. Inparticular, since as illustrated in FIG. 4, natural gas combusts at adifferent rate than diesel fuel, strategies of the present disclosuremay advance or retard the timing of diesel fuel injection, or advance orretard the timing of natural gas injection during the piston cycle. Suchan injection strategy may result in a dual fuel peak pressure and/or adual fuel torque output that substantially matches the diesel fuel onlypeak pressure and/or a diesel fuel only torque output. For example,system 100 may be configured to execute a dual fuel injection strategyin which, at a given engine load, the torque or power output ofcombustion chamber 62 is approximately equal to a corresponding torqueor power output of combustion chamber 62 when only diesel fuel iscombusted therein.

To achieve the injection strategies described above, at 206 controlsystem 50 may determine a combined injection pulse based on, among otherthings, the diesel injection pulse determined at 204. In an exemplaryembodiment, first controller 52 may generate a signal indicative of thediesel injection pulse and may transmit such a signal to secondcontroller 54. Second controller 54 may be configured to determine thecombined injection pulse at 206 based on the diesel injection pulsesignal received from first controller 52. Alternatively, firstcontroller 52 may generate a signal indicative of the diesel injectionpulse and may transmit such a signal to components of fuel system 36 inorder to facilitate injection of diesel fuel only. In exemplaryembodiments in which such a signal is directed from first controller 52to fuel system 36, second controller 54 may be configured to interceptsuch a signal and to determine a combined injection pulse at 206 basedon such a signal. In such embodiments, the determination of the dieselinjection pulse by first controller 52 may be unaffected by, forexample, determination of the combined injection pulse at 206 and/or byoperations of second controller 54.

In exemplary embodiments, the combined injection pulse determined at 206may be indicative of a second amount of diesel fuel to be injecteddifferent than the first amount of diesel fuel associated with thediesel injection pulse. The combined injection pulse may also beindicative of a second timing at which the second amount of diesel fuelis to be injected, and such a second timing may be different than thefirst timing associated with injection of the first amount of dieselfuel. Additionally, the combined injection pulse may be indicative of anamount of natural gas to be injected and a timing at which the amount ofnatural gas is to be injected. Accordingly, in exemplary embodiments ofthe present disclosure, the combined injection pulse may comprise asingle injection pulse or multiple injection pulses. In embodiments inwhich the combined injection pulse comprises multiple injection pulses,the combined injection pulse may comprise a pair of fuel injectionpulses associated with a dual fuel injection/combustion strategy. Insuch embodiments, one of the dual fuel injection pulses may beindicative of an amount of diesel fuel to be injected and a timing atwhich the amount of diesel fuel is to be injected, and another of thedual fuel injection pulses may be indicative of an amount of natural gasto be injected and a timing at which the amount of natural gas is to beinjected. Thus, for purposes of this disclosure, the terms “combinedinjection pulse” and “dual fuel injection pulse(s)” may be usedinterchangeably. In exemplary embodiments, first controller 52 maydetermine the diesel injection pulse at 204 in conjunction with and/orcorresponding to determining a variety of other demanded controlparameters including an amount of turbo boost to be provided by turbine28, an amount of exhaust gas to be recirculated to induction system 16,and/or other like parameters. Accordingly, since second controller 54determines the combined injection pulse at 206 based on the dieselinjection pulse, second controller 54 inherently determines the combinedinjection pulse based on these additional demanded control parameters.

In exemplary embodiments, second controller 54 may determine thecombined injection pulse at 206 in response to receiving and/orintercepting a signal from first controller 52 indicative of the dieselinjection pulse. Further, it is understood that the amount and/or timingof diesel fuel injection associated with the combined injection pulsedetermined at 206 may be different than the corresponding amount and/ortiming of diesel fuel injection associated with the diesel injectionpulse determined at 204. For example, the timing of diesel fuelinjection associated with the combined injection pulse may be earlier ina piston cycle of combustion chamber 62 than the timing of the dieselfuel injection associated with the diesel injection pulse determined at204. It is also understood that the timing natural gas injectionassociated with the combined injection pulse determined at 206 may beearlier, later, and/or otherwise different than the timing of dieselfuel injection associated with the combined injection pulse.

In each of the exemplary embodiments described above, second controller54 may determine the combined injection pulse at 206 utilizing one ormore lookup tables stored in a memory associated with control system 50.Exemplary lookup tables 78, 80, 82 are illustrated in FIG. 5. Forexample, upon receiving and/or intercepting a signal indicative of thefirst diesel amount associated with the diesel injection pulse, and asignal indicative of current engine speed, second controller 54 mayreference one or more of lookup tables 78, 80, 82 to identify a seconddiesel amount, a second diesel timing a natural gas amount, and anatural gas timing corresponding to the first diesel amount and currentengine speed. In such embodiments, current engine speed and the first(i.e., commanded) diesel amount of the diesel injection pulse may beused by second controller 54 as inputs to one or more of lookup tables78, 80, 82, and the second diesel amount, second diesel timing, naturalgas amount, and natural gas timing may comprise corresponding lookuptable outputs.

In further exemplary embodiments, at least one of intake air temperatureand ambient air temperature determined by sensors 56 may be may be usedby second controller 54 as inputs to one or more of lookup tables 78,80, 82, or as inputs to an algorithm or control protocol associated withdetermining the combined injection pulse. In such embodiments, thesecond diesel amount, second diesel timing, natural gas amount, andnatural gas timing associated with the combined injection pulse may bedetermined at 206 based on the at least one of intake air temperatureand ambient air temperature. For example, at 206, second controller 54may receive one or more signals from sensors 56 indicative of at leastone of intake air temperature and ambient air temperature, and mayselect, based on the at least one of intake air temperature and ambientair temperature, a set of lookup tables for use in determining thecombined injection pulse. For instance, at 206, second controller 54 maycompare the at least one of intake air temperature and ambient airtemperature to corresponding temperature thresholds or to correspondingtemperature ranges. As illustrated in FIG. 5, such ranges may include ahigh temperature range, a medium temperature range, and a lowtemperature range. At 206, second controller 54 may select thetemperature range or temperature threshold to which the at least one ofintake air temperature and ambient air temperature corresponds, and mayutilize the lookup tables associated with the selected temperature rangeor temperature threshold to determine the second diesel amount, seconddiesel timing, natural gas amount, and natural gas timing associatedwith the combined injection pulse. As described above, the second dieselamount, second diesel timing, natural gas amount, and natural gas timingassociated with the combined injection pulse may be outputs of theselected one or more lookup tables.

At 208, fuel system 36 may be controlled by control system 50 to injectdiesel fuel and natural gas into combustion chamber 62 in accordancewith the combined injection pulse determined at 206. For example, at 208the second amount of diesel fuel determined in association with thecombined injection pulse may be injected into combustion chamber 62 atthe corresponding second injection timing determined at 206.Additionally, at 208 the amount of natural gas determined in associationwith the combined injection pulse may be injected into combustionchamber 62 at the corresponding natural gas injection timing determinedat 206. In each of the exemplary embodiments described herein, injectingthe second amount of diesel fuel and the amount of natural gas into thecombustion chamber 62 in accordance with the combined injection pulsedetermined at 206 may result in a combustion event within the combustionchamber 62 characterized by a second combustion characteristic that issubstantially equivalent and/or otherwise equal to the first combustioncharacteristic described above. For example, injecting both diesel andnatural gas into combustion chamber 62 in accordance with the combinedinjection pulse may result in a peak pressure being generated withincombustion chamber 62 that is substantially equal to the peak pressuredescribed above with respect to point A of FIG. 4 (i.e., in aconfiguration in which only diesel fuel is combusted in engine 10),and/or a desired torque output.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed fuel system.Other embodiments will be apparent to those skilled in the art fromconsideration of the specification and practice of the disclosed fuelsystem. It is intended that the specification and examples be consideredas exemplary only, with a true scope being indicated by the followingclaims and their equivalents.

1-15. (canceled)
 16. An engine controller, comprising: a sensor inputconfigured to receive a sensor signal indicative of an operatingparameter associated with an engine; and a processor configured toperform operations including: obtaining injection pulse informationassociated with the operating parameter, wherein the injection pulseinformation includes a first quantity of fuel, a first timing, a secondquantity of fuel, and a second timing; generating a first fuel injectioncontrol signal in accordance with injection pulse information to injectthe first quantity of fuel into an engine cylinder in accordance withthe first timing; and generating a second fuel injection control signalin accordance with injection pulse information to inject the secondquantity of fuel into the engine cylinder in accordance with the secondtiming.
 17. The engine controller of claim 16, wherein obtaining theinjection pulse information includes: determining a required engineoutput based, at least in part, on the operating parameter; anddetermining the injection pulse information based on the required engineoutput and an engine parameter selected from: engine speed, engine load,accelerator pedal position, brake pedal position, and transmission gear.18. The engine controller of claim 16, wherein the operating parametercomprises a temperature parameter.
 19. The engine controller of claim18, wherein the temperature parameter is indicative of a temperature ofintake air directed to the engine.
 20. The engine controller of claim18, wherein the temperature parameter is indicative of an ambient airtemperature.
 21. The engine controller of claim 18, wherein thetemperature parameter comprises an exhaust temperature parameterindicative of a temperature of exhaust emitted by the engine.
 22. Theengine controller of claim 16, wherein the first fuel injection controlsignal controls injection of a first fuel into an engine cylinder andthe second fuel injection control signal controls injection of a secondfuel into the engine cylinder, wherein the first fuel and the secondfuel are different.
 23. The engine controller of claim 22, wherein thefirst fuel is a gaseous fuel.
 24. The engine controller of claim 23,wherein the gaseous fuel includes methane.
 25. The engine controller ofclaim 23, wherein the gaseous fuel includes natural gas.
 26. The enginecontroller of claim 23, wherein the second fuel is a liquid fuel. 27.The engine controller of claim 26, wherein the liquid fuel includesdiesel fuel.
 28. The engine controller of claim 26, wherein the liquidfuel includes gasoline.
 29. An engine control method, comprising:receiving a sensor signal indicative of an operating parameter of anengine; accessing single-fuel injection pulse information indicative ofa single-fuel injection pulse in accordance with the operatingparameter; determining a combustion characteristic in accordance withthe single-fuel injection pulse; determining a combined-fuel injectionpulse, including a first injection pulse associated with a first fueland a second injection pulse associated with a second fuel, inaccordance with the combustion characteristic; and providing, for eachpiston cycle, the first injection pulse to a first fuel injectorassociated with the first fuel and the second injection pulse to asecond fuel injector associated with the second fuel.
 30. The enginecontrol method of claim 29, wherein the first injection pulse controls afirst fuel injector configured to inject the first fuel and wherein thesecond injection pulse controls a second fuel injector configured toinject the second fuel.
 31. The engine control method of claim 29,wherein the operating parameter comprises an engine speed of the engine.32. The engine control method of claim 29, wherein the operatingparameter comprises a vehicle speed of the engine of a vehicleassociated with the engine.
 33. The engine control method of claim 29,wherein the operating parameter comprises an engine load parameter. 34.The engine control method of claim 29, wherein the operating parameteris a temperature parameter and wherein the temperature parameter isselected from a group consisting of: intake temperature, ambienttemperature, and exhaust temperature.
 35. The engine control method ofclaim 29, wherein the operating parameter comprises an exhaust pressure.36. The engine control method of claim 29, wherein the combustioncharacteristic comprises a combustion chamber peak pressure.
 37. Theengine control method of claim 29, wherein the combustion characteristiccomprises a torque output associated with the combustion chamber.
 38. Amotorized vehicle, comprising: an engine, affixed within the vehicle;and an engine controller configured to: determine an operating parameterof the engine; determine a single fuel injection pulse based on theoperating parameter; determine a combustion characteristic associatedwith the single fuel injection pulse; determine dual-fuel injectionpulses, including a first injection pulse to deliver a first quantity ofa first fuel to a combustion chamber at a first timing and a secondinjection pulse to deliver a second quantity of a second fuel to thecombustion chamber at a second timing, that generate the combustioncharacteristic; and providing, during each piston cycle, the firstinjection pulse to a first fuel injector and the second injection pulseto a second fuel injector.